Wait for task

Table of Content

Wait for task#

Wait task to complete with timeout When a timeout occurs the wait_for function cancel the task and raise asyncio.Timeout exception

import asyncio
import logging
import time

async def wait_func(text, delay=2):
    await asyncio.sleep(delay)


async def main():
    task1 = asyncio.create_task(wait_func("task1", delay=5))

    try:
        await asyncio.wait_for(task1, timeout=2)
    except asyncio.TimeoutError:
        print("task cancelled by timeout")


asyncio.run(main())

Wait#

The asyncio.wait() function runs an iterable of awaitables objects and blocks until a specified condition.

Condition	Description
FIRST_COMPLETED	Return when all awaitables are complete or canceled.
FIRST_EXCEPTION	Return when any awaitable is raising an exception
ALL_COMPLETED	Return when all awaitables are complete or cancelled.

done, pending = asyncio.wait(aws, *, timeout=None, return_when=ALL_COMPLETED)

done: Set of a awaitables that are done
pending: Set of a awaitables that are pending

Demo#

ALL_COMPLETED

import asyncio
import logging
import time

logging.basicConfig(format="%(asctime)s %(message)s", level=logging.DEBUG, datefmt='%H:%M:%S')
log = logging.getLogger(__name__)

async def wait_func(text, delay=2):
    log.info(f"start {text}")
    await asyncio.sleep(delay)
    log.info(f"end {text}")


async def main():
    start = time.perf_counter()
    task1 = asyncio.create_task(wait_func("task1", delay=3))
    task2 = asyncio.create_task(wait_func("task2", delay=2))
    task3 = asyncio.create_task(wait_func("task3", delay=5))

    done, pending = await asyncio.wait([task1, task2, task3], return_when=asyncio.ALL_COMPLETED)

    end = time.perf_counter()
    log.info(f'It took {round(end-start,0)} second(s) to complete.')


asyncio.run(main())

10:26:39 start task1
10:26:39 start task2
10:26:39 start task3
10:26:41 end task2
10:26:42 end task1
10:26:44 end task3
10:26:44 It took 5.0 second(s) to complete.

xxx#

Reference#

asyncio.wait